1. Field of the Invention: The present invention relates generally to a bracing device for a self-advancing shield tunnelling machine for tunnel construction and, more particularly, to a bracing device which is composed of a control shield within which is mounted a cutting unit, and at least two bracing shields which are connected together by feed cylinders, the bracing shields being able to be radially braced with the tunnel wall independently of one another by bracing elements which are fixed thereto.
2. Description of the Prior Art: In tunnel construction, shield machines are usually driven with tubbing support of sliding lagging, and in canal construction, especially in an inaccessible area, by tube driving. In the typical tunnel construction process, the advancing of the machine occurs via feed cylinders which are supported on the newly produced tunnel lining or tubbing. The machine direction control normally occurs via operation of the feed cylinders or via special piston valve cylinders, through which operation an articulatedly connected control shield is moved forward in the desired direction.
In known shield machines in which the bracing required for advancement of the machine is carried out in an area in which there is not yet any tubbing, bracing typically occurs by radially outwardly movable single elements or by expanding shields which form movable parts of the shield wall construction. As a result of the necessary relative movement between the moving and fixed elements of the shield wall construction, gaps are formed between the moving and fixed elements through which leakages may easily occur. Shield machines with radially movable bracing elements frequently have advancing mechanisms which possess two shields or bracing members, namely, one bracing member in which is mounted a boring head that is moved forwardly out of the shield via feed cylinders, and a second bracing member which serves to advance the first bracing plane. The second bracing member, for its part, can also be drawn up over the first bracing member. It is also known for areas to be provided between the bracing members in which the shields telescopically overlap. Such machines, which are most suitable for use in stable ground (particularly hard rock) there is a danger of holing occurring immediately behind the boring head and in front of the first shield if the machines are used in loose, friable and flexible ground. If these machines are used in unstable ground, it is necessary to advance the first bracing unit together with the boring head via the second bracing unit.
An advantage exists, therefore, for a self-advancing shield tunnelling machine having bracing elements of uncomplicated construction which prevent the occurrence of gaps and leakages when the bracing elements are radially outwardly extended.
A further advantage exists for a self-advancing shield tunnelling machine having first and second brace members which will permit a boring head supported by the first brace member to be advanced independently of the first brace member.
It is therefore an object of the present invention to provide bracing elements for a self-advancing shield tunneling machine wherein the bracing elements are of uncomplicated construction and prevent the occurrence of gaps and leakages when the bracing elements are radially outwardly extended.
It is a further object of the present invention to provide a self-advancing shield tunneling machine having first and second bracing members which will permit a boring head supported by the first brace member to be advanced independently of the first brace member.
Still other objects and advantages of the present invention will become apparent in light of the attached drawings and written description of the invention presented herebelow.